Creeping thyme

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For several years I have been observing wild creeping thyme which I have collected from manysources, both in Britain and in Europe.  I have become convinced that the two species Thymus serpyllum, with hairs on four sides of the stem and T. polytrichus subsp. britannicus, with hairs on two sides of the stem, are in fact all one species and not two as defined by botanists.  There is far too much similarity between the two so-called species, but also too much dissimilarity within each species.  Thymus serpyllum of southern Europe differs from that of north west Europe and Britain, in that the leaves are much bigger and the stems much longer.  There is debate as to the exact nature of the type specimen described by Linnaeus and his description is very brief, with no mention of hair distribution on the stems.  Although botanists state that T. serpyllum only occurs in Breckland in Britain, there are other wild collected plants with the same growth pattern as Breckland thyme, with hairs on four sides of the stem, such as T. serpyllum 'Vey' which was collected in Scotland and there is also the cultivar T. 'Bethany'(Coccineus Group).  Plants collected in Carsington, Derbyshire, exhibit similar growth pattern, but have hairs on two sides of the stem.

Thymus pulegioides
, which is widespread throughout Europe, varies from a very compact low growing plant with small leaves, to a large loose bush with long trailing stems and large leaves, but with very similar DNA in the thymes which Dr. Madan Thangavelu and I have tested.  This has lead me to the hypothesis that there could also be similar diversity within the creeping thyme of north west Europe.  In the introduction to Flora Iranica in 1982, Jalas wrote "Indumentum characters, including stem hairiness (whether hairy all round, on two opposite sides or along the four angles alone), are of limited taxonomical value."  This was written after he wrote the Thymus descriptions in Flora Europaea.  In 1970 in Veröffentlichungen des Geobotanischen Institutes der eth Stiftung Rübel (Zürich), writing about T. longicaulis, he referred to confusion with T. serpyllum which he regarded as being restricted to north eastern France.

Based on my study of the wild collected thyme in my Collection and on the writings of Jalas, I proposed in 2009 in The Thyme Handbook that the wild creeping thyme of Britain and Scandinavia should all be regarded as T. serpyllum.  As far as the larger leaved, so-called T. serpyllum, of central and southern France, is concerned I will await the results of the Creeping Thyme DNA Study.  Dr. Madan Thangavelu is using thymes I have collected in France, in the Dordogne and also in Austria, which all have much larger leaves than the creeping thyme collected in Britain and these will also be compared with European species such as T. longicaulis and T. pannonicus.

There are several cultivars with long prostrate stems, which have been included in T. serpyllum, such as T. 'Flossy', T. 'Iden', T. 'Lemon Curd' and T. 'Rainbow Falls'.  As they are more likely to be related to European Thymus species, they are better referred to without the specific epithet.

As far as the hairy leaved thymes are concerned, I have observed both hairy and non-hairy creeping thymes growing side by side in the wild and consider that it could be an adaptation to climatic conditions.  In Snowdonia the proportion of hairy leaved thyme is greater in plants growing at a higher altitude.  When examined with a hand lens it can be seen that the amount of hairiness on the leaves varies considerably.  The margins can be ciliate or just ciliate at the base, the upper surfaces vary from glabrous, to sparsely covered with white hairs or thickly covered and the lower surfaces likewise.  Wilmott in 1923 considered Miller's 1768 T. lanuginosus a name of doubtful status because of the inability to locate a type specimen in the herbarium of Miller.  Ronniger in 1924 described British woolly thyme as T. lanuginosus, but in 1927 published the new name T. pseudolanuginosus for this thyme.  I was given access to the specimen in the Druce Herbarium at Oxford, which Ronniger used for his citation of T. pseudolanuginosus and discovered that it was less hairy than many of the wild specimens I have collected in England and Wales!  Harriet Flannery in 1982, in A Study of the Taxa of Thymus Cultivated in the United States, considered that there were insufficient grounds for designating Ronniger's T. pseudolanuginosus as an independent species and proposed the cultivar epithet 'Lanuginosus' within T. praecox subsp. arcticus.  However in view of the fact that there is such a wide variation in the amount of hairiness present in wild thyme populations and it is next to impossible to delineate between the hairy and non-hairy creeping thymes, I proposed in 2009, in The Thyme Handbook, that they should all be regarded as T. serpyllum.

For pictures showing variation in leaf hairiness in wild collected T. serpyllum. click 

 Updated May 2010
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